It found those who worked in outdoor jobs or enjoyed outdoor activities had a significantly reduced risk of breast cancer.

Study leader Dr Julia Knight said: "Evidence is growing that vitamin D might help reduce the risk of breast cancer, and what we see is consistent with the idea that what occurs during breast development in adolescence may influence future breast cancer risk."

Consumption of cod liver oil for 10 years or more was also associated with a lower risk of breast cancer, as was consumption of more than nine glasses of milk per week at the ages of 20 to 29.